Would you guys prefer FB20 or FB25 for NA FT?

[JohnnyR]

Originally Posted by Exage

Is a 2.0L a 2.0L. No! Look at my 2ZZ-GE Vs. a 1ZZ-FE. Both displace 1.8L, both are very different animals... I'd be happy to try and explain it in more detail on the engine tech thread if you'd like!

I had a 2000 Celica GT-S and boy was that motor fun to rev out with my Kazuma exhaust lol. Sounded incredible. The "cam-change" like people called it was a neat experience, the change in tone and engine pull was fun. Unfortunately we probably won't be getting that here.

I'm fine with either honestly. Love boxer's sounds and characteristics, hate working on my friends cars though heh. It was a logical choice for them for the handling benefits of course. Wish this was turbo, but eh, it is what it is.

[old greg]

Originally Posted by Dimman

Could end up being that an FB25's bore with this 1.6's crank (assuming it's a high performance short stroke motor to meet WRC requirements) could end up being 2.0L.

I've been thinking about this today so I did some quick math. The FB20 has a bore of 84mm and a stroke of 90mm. If the rumored 1.6L WRX uses the same block it would have a 72mm stroke. That crankshaft with the 94mm bores of the FB25 block would displace 1.998L.

I think it's entirely plausible, given the coming CAFEpocalypse, that both the WRX and STi will get downsized and direct injected for 2012, with this short stroke 2L in the STi.

[Allch Chcar]

Originally Posted by old greg

I've been thinking about this today so I did some quick math. The FB20 has a bore of 84mm and a stroke of 90mm. If the rumored 1.6L WRX uses the same block it would have a 72mm stroke. That crankshaft with the 94mm bores of the FB25 block would displace 1.998L.

I think it's entirely plausible, given the coming CAFEpocalypse, that both the WRX and STi will get downsized and direct injected for 2012, with this short stroke 2L in the STi.

It would probably get the same crank from the 2.5L just a different bore. That's what the EL15 has and it has a 77mm bore.

Narrower bore, longer stroke. That's what they did with the EL15 back in 2006 and it looks like that is what they did for the FB20 too.

[Dimman]

Originally Posted by old greg

I've been thinking about this today so I did some quick math. The FB20 has a bore of 84mm and a stroke of 90mm. If the rumored 1.6L WRX uses the same block it would have a 72mm stroke. That crankshaft with the 94mm bores of the FB25 block would displace 1.998L.

I think it's entirely plausible, given the coming CAFEpocalypse, that both the WRX and STi will get downsized and direct injected for 2012, with this short stroke 2L in the STi.

Both these hypothetical 84mm X 72mm 1.6L and 94mm X 72mm 2.0L would be awesome for revs, turbo or not.

(Please come true, please come true, please come true...)

[tranzformer]

Originally Posted by old greg

I've been thinking about this today so I did some quick math. The FB20 has a bore of 84mm and a stroke of 90mm. If the rumored 1.6L WRX uses the same block it would have a 72mm stroke. That crankshaft with the 94mm bores of the FB25 block would displace 1.998L.

I think it's entirely plausible, given the coming CAFEpocalypse, that both the WRX and STi will get downsized and direct injected for 2012, with this short stroke 2L in the STi.

That sounds very interesting. What kinda of redline would you have with a theoretical build like this?

[old greg]

Originally Posted by Allch Chcar

It would probably get the same crank from the 2.5L just a different bore. That's what the EL15 has and it has a 77mm bore.

That worked because the 2.5L was quite oversquare to begin with. The FB20 and FB25 share a 90mm stroke crank. This crank in a 1.6L would need a bore size of 75mm. If there will be a 1.6L wrx, that doesn't seem like enough valve area for a car with ~250 hp from the factory.

Originally Posted by tranzformer

That sounds very interesting. What kinda of redline would you have with a theoretical build like this?

In terms of mean piston speed you could hit 10500 and still be under the current "limit" of ~5000 feet per minute. But you'll be limited by a lot of other things first, mainly the bearings and the oiling system. This is true of every engine.


Honestly, now that I've had some time to think about it, a 72mm crank is massive overkill in the RPM department. But I do believe that a downsized WRX/STi would be destroked, just maybe not that much.

[Allch Chcar]

Originally Posted by old greg

That worked because the 2.5L was quite oversquare to begin with. The FB20 and FB25 share a 90mm stroke crank. This crank in a 1.6L would need a bore size of 75mm. If there will be a 1.6L wrx, that doesn't seem like enough valve area for a car with ~250 hp from the factory.



In terms of mean piston speed you could hit 10500 and still be under the current "limit" of ~5000 feet per minute. But you'll be limited by a lot of other things first, mainly the bearings and the oiling system. This is true of every engine.


Honestly, now that I've had some time to think about it, a 72mm crank is massive overkill in the RPM department. But I do believe that a downsized WRX/STi would be destroked, just maybe not that much.

I dunno, would it work if it was a narrow angle head? The Honda Lea(L15 vtec) is capable of 250BHP with a turbo on a stock head I think huh?

The mean piston speed isn't the problem with subaru's engines. Their crank generates a lot of harmonic imbalance vibrations around 8500RPM. Would have to ask Ichitaka or some of the Subaru engine building experts ...

[old greg]

Originally Posted by Allch Chcar

The Honda Lea(L15 vtec) is capable of 250BHP with a turbo on a stock head I think huh?

I wouldn't know. I'd assume though that at those power levels the head is becoming a bottle-neck. That's acceptable for an engine that started out with half that horsepower, but for a performance engine in an oft modified car it doesn't make sense to have such limited room for improved performance. Not everyone modifies their WRX's, I haven't, but these kinds of cars sell based on their reputations, and their horsepower potential is a big part of that.

[Allch Chcar]

Originally Posted by old greg

I wouldn't know. I'd assume though that at those power levels the head is becoming a bottle-neck. That's acceptable for an engine that started out with half that horsepower, but for a performance engine in an oft modified car it doesn't make sense to have such limited room for improved performance. Not everyone modifies their WRX's, I haven't, but these kinds of cars sell based on their reputations, and their horsepower potential is a big part of that.

Definitely. But if it was a turboed engine with a more sporty design than it could be different right? I probably I shouldn't get my hopes up. No one would make that anyway .

There are plenty of sporty engines in the 2liter+ range. Everything smaller is usually reserved for DD and fuel sippers. Honda is the only company with any good new sub2liters for cars nowadays.

It sucks being stuck interested in a niche inhabited by FWD DD . Besides the Miata and the up and coming FT-86, there is only classic cars in the subcompact, lightweight RWD category. Technically the BMW 1-series and Hyundai Genesis Coupe are considered subcompacts by the EPA , but both are ridiculously heavy.

[old greg]

Originally Posted by Allch Chcar

Besides the Miata and the up and coming FT-86, there is only classic cars in the subcompact, lightweight RWD category.

Don't forget the Smart Fortwo.

And for people with too much money, the Alfa 4C GTA is supposedly coming stateside. I may need to sell a kidney or two.

[Dimman]

Allch Chcar: Compare our hypothetical 84mm X 72mm to the 4AGE's real 81mm X 77mm bore x stroke.

All motor 1.6L 16v 4AGE's made 240hp all motor in Formula Atlantic.

Our hypothetical motor could have more valve area (larger bore), and safely rev higher (less stroke) to take advantage of the extra flow.

A little call to Yamaha, and yum!

Mmmmm... hypothetical motor...

[MannyO]

First off, I just wanna say much to all of you who clearly know a lot more about engines that I. It's therapeutic to read the really technical stuff on here so thanks.

Back on topic, Dimman, you mentioned Yamaha. You're referring to the heads/head work right?

[Dimman]

Originally Posted by MannyO

First off, I just wanna say much to all of you who clearly know a lot more about engines that I. It's therapeutic to read the really technical stuff on here so thanks.

Back on topic, Dimman, you mentioned Yamaha. You're referring to the heads/head work right?

Still a rumour, as far as I know. Technically this is a Subaru motor, so it's hard to guess how the technical relationship will work. Historically speaking, Yamaha should be helping Toyota out for this motor.

The confirmed motors that have had Yamaha help that I can think of of the top of my head are the 4AG(Z)E, 3SG(T)E, 1JZG(T)E, 2ZZGE and the 1LRGUE. Could be others I'm missing. And I do know that the 2000GT's L6 was a complete Yamaha design back in the day.

[MannyO]

Thanks for the clarification.